Goodwill and Intangible Assets - Goodwill Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	$ 488,602	$ 255,876
Acquisitions and adjustments	12,934	232,726
Goodwill, net of accumulated impairments, ending balance	501,536	488,602
Brooks Semiconductor Solutions Group
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	47,847	47,963
Acquisitions and adjustments	512	(116)
Goodwill, net of accumulated impairments, ending balance	48,359	47,847
Brooks Life Sciences Products
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	101,957	104,212
Acquisitions and adjustments	1,321	(2,255)
Goodwill, net of accumulated impairments, ending balance	103,278	101,957
Brooks Life Sciences Services
Goodwill [Roll Forward]
Goodwill, net of accumulated impairments, beginning balance	338,798	103,701
Acquisitions and adjustments	11,101	235,097
Goodwill, net of accumulated impairments, ending balance	$ 349,899	$ 338,798